please also include examples for each, thank you.

3. [6 Points] Six friends are going to the movies. One of them is a doctor on call, another is an icognito movie star. (a) In how many ways can they be seated in a row of six seats? (b) In how many ways can they be seated if the doctor must be seated in one of the two aisle seats of the row? (c) In how many ways can they be seated if the doctor needs an aisle seat and, to remain concealed, the movie star needs an inner seat (not on the aisles)